We will investigate the role of: 1) turnover of liver pyruvate kinase protein, 2) covalent modification of liver pyruvate kinase and, 3) variations in the concentration of specific substrates and effectors of the enzyme in the in vivo regulation of pyruvate kinase activity in liver. We will examine pyruvate kinase isolated from the livers of intact animals that have been subjected to dietary and hormonal stress. Incorporation of radioactive amino acids into the enzyme will be used to determine the importance of specific protein synthesis and degradation. Kinetic, chemical and physical properties of the enzyme will be correlated to changes in activity levels in response to overall changes in net carbohydrate flux.